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Largest refracting telescopes in the world

Refractors are limited by the laws of physics. Gravity bends the lens’ perfect shape, deforming it as the telescope is pointed to different parts of the night sky. The insurmountable problem of providing support to the lens at its centre meant that a limit of around half a metre would put paid to larger lenses being constructed.

The largest refractor in existence today is the mighty Yerkes near Chicago in the United States. Its 40-inch lens was lovingly figured by the Clark brothers in 1897.

For several years the Craig Telescope was to be the largest in the world.

Despite this limitation, refractors have the advantage over reflectors in that there is no central obstruction which lowers the contrast of planetary detail and spreads starlight, preventing astronomers examining close binary stars.

Refracting telescopes were not completely abandoned when huge leaps in aperture were accomplished by the reflector in the first part of the 1900s. Indeed several “large” refractors were constructed as late as 1942!

What follows is a list of the largest refractors ever built. Some have been dismantled, some destroyed and some relocated. However, many are still in operation today.

Diam(ins)

Diam(m)

Year

Description

Country

49.0ins

1.25m

1900

Mounted horizontally with a sidereostat mirror 2 meters in diameter placed in front. Disassembled after the Paris exhibition in November 1900.More>>